This thesis investigates criteria used by research agencies that publish ratings of business organisations in respect of their corporate social responsibility (CSR) performance and the relationship of these criteria to underlying ethical principles. Companies are rated according to CSR criteria. Observation of different rating agencies' results for the same, or similar organisations, shows a significant variation in results. Variations in rating must result either from different criteria being applied or from criteria addressing similar topics being assessed in a different way. Criteria from different rating agencies are found to be comparable. Thus if rating criteria are derived from an ethical view of the responsibilities of business organisations, then inconsistent results may be explained by variations in the ethical basis of corporate social responsibility used by agencies. Subject companies are rated under broad categories such as corporate governance, human rights and the environment. These categories contain specific criteria. My investigation compares the criteria used by major rating agencies and identifies the ethical basis, if any, that can be attributed to each criterion. The study finds that there are clearly identifiable links between a number of criteria used by each rating agency and the ethical theories selected for evaluation. Further, there is sufficient difference between the agencies to characterise each in relation to one or more of the ethical theories selected. There is inconsistency, however, within each agency's basis of principles as well as between agencies, which indicates an unsatisfactory lack of explicit relationship between the general, and reasonably consistent, definition of corporate social responsibility and application of coherent ethical principles. In practical terms around 10% of all investments in the United States, representing 2.3 trillion dollars, are invested in ethical or screened funds that rely on these and similar rating agencies results to determine CSR performance of firms. The large variation in results demonstrated in my thesis suggests that very significant financial decisions are based, at least in part, on inconsistent data. I suggest in my conclusion that if agencies were to consider, justify and clearly state the ethical basis from which their criteria derive, then investment managers and their clients could be more certain that their CSR principles were being upheld.